In general, a metal compound is added as a reaction catalyst in order to promote a polymerization reaction during polymerization of polymer compounds. The metal compound remains in the polymer after the polymerization reaction. The remaining metal catalyst compound acts as a main factor that generates cracks on a film and reduces transparency during the production of the polymer film. Furthermore, a high temperature is required during molding of polymer products, and there are problems in that the polymer is discolored or decomposed due to the catalyst compound which is present at high temperatures, significantly reducing physical properties thereof. Accordingly, there remains a need to provide a method of removing the remaining metal catalyst compound after the polymerization of the polymer due to the above-mentioned reasons.
Examples of a method of removing a metal catalyst compound from a polymer solution include a method of performing treatment by using a solution mixture of an excessive amount of a hydrochloric acid and ethanol or an excessive amount of sodium hydroxide solution. However, removal efficiency of the metal catalyst compound from the polymer solution is not high, a separate neutralization process is required because an excessive amount of acid or base is used, and there are problems in views of safety of equipment and an environment. Therefore, the method is not desirable.
In another method, a metal compound is extracted by using a substance that is capable of extracting a metal catalyst compound present in the polymer solution in a solution state, and then separated from the polymer solution to remove a solution layer from which the metal compound is extracted and to obtain a clean polymer solution. However, a great amount of substance is used to extract the metal catalyst compound, and it is required that a process of treating the extraction substance is separately performed.
Furthermore, there is a method of using an ion exchange resin. In the method, an ion exchange resin that has a strong basic or strong acidic functional group is added in a state where a metal catalyst compound is present in a polymer solution to remove the metal catalyst compound. However, since there are problems in that removal efficiency of the catalyst compound is low, a strong acid and a strong base must be used during regeneration of the used ion exchange resin, and a price of ion exchange resin is high, it is difficult to commercialize the method.
If a chelate compound of the metal catalyst compound is formed by using a chelate, precipitated, and filtered, the metal catalyst compound is easily removed. However, there are problems in that a filtration material must be used during the filtration process and periodically replaced because a filtering speed is reduced as the number of filtration is increased due to a process characteristic. Furthermore, in the case of when selection of the chelate is not preferable, removal efficiency of the metal catalyst compound may be very low, and a phase separation may occur in respect to a polymer that is dissolved in a solvent due to a polar functional group of the chelate.
In the case of when an inorganic filler having a polar functional group is added to a polymer solution in order to avoid the above-mentioned problems of the filtration material, a chelate of a metal catalyst compound of the solution and the functional group of the inorganic filler is formed so that only the inorganic filler is filtered to remove the metal catalyst compound, thus a subsequent process of using the filtration material is not required. However, since the price of the inorganic filler having the functional group is very high, this process is difficult to be commercialized.